RFR: 8264999: GeneralPath.lineTo() to itself produces jagged lines

[Jeremy]

Previously when you drew a line that moved exactly (+0, +0) with a miter stroke the Stroker class acted like a horizontal miter was appropriate. Now we abort instead, so no miter is applied.

The new unit test tests the original steps plus several variations.

I'm a little nervous about this change because it looks like someone previously considered this exact condition and implemented a different behavior. I don't think I understand the original rationale.

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Commit messages:
 - JDK-8264999: GeneralPath.lineTo() to itself produces jagged lines
 - Merge pull request #3 from openjdk/master
 - Merge pull request #2 from openjdk/master
 - Merge pull request #1 from openjdk/master

Changes: https://git.openjdk.java.net/jdk/pull/8943/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8943&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264999
  Stats: 218 lines in 2 files changed: 217 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8943.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8943/head:pull/8943

PR: https://git.openjdk.java.net/jdk/pull/8943